The PDP undergoes, e.g. the following steps before it is completed: forming of an electrode layer on the surface of a substrate such as a glass board, then forming of a dielectric layer covering the electrode layer, and forming of a protective film made of MgO on the dielectric layer.
The following methods have been conventionally known as the method of forming the protective film: a method of applying MgO paste and sintering the paste, or an evaporating method or a sputtering method using electron beam or ion beam. The evaporating method using electron beam has been widely used among others because this method can form the MgO film of better quality at a higher speed. (For instance, refer to “FPD technology compendium 2001” published by Electronic Journal Inc. in Oct. 25, 2000, at pp 598-600.)
When a film is formed on a PDP substrate, the substrate should be held steadily in an evaporating room, or the substrate should be transported in/out the evaporating room steadily. Thus the substrate is generally held by a substrate holder. The material of film naturally attaches to the holder when the film is formed on the substrate, and forms a sheet of the film also on the holder.
It is important to make the conditions, such as a degree of vacuum, stable within the evaporating room for obtaining steady quality of the film. However, the substrate holder, as discussed above, goes back and forth between the evaporating room and the atmosphere, and the film material attached to the surface of the holder absorbs well gasses and water. Therefore, the holder becomes a factor to change substantially the conditions, such as a degree of vacuum, within the evaporating room.
In order to decrease the influence of the holder to the conditions in the evaporating room, the holder attached with the film material, which emits gas, is replaced with another holder free from the film material attached, so that an amount of gas emitted in the evaporating room can be reduced. As a result, the conditions, such as a degree of vacuum, in the evaporating room is kept steady.
However, even if the things go along the way to lower an amount of gas emitted in the evaporating room and improve the conditions in the evaporating room, a great change in the conditions will vary the quality of the film formed. As a result, a greater disperse occurs in the characteristics of the PDP.
The present invention addresses the problems discussed above, and aims to achieve a PDP manufacturing method which can form a sheet of quality film by controlling appropriately the conditions in the evaporating room.